1. Field of the Invention
The present invention relates to a device and a method for manufacturing a work. More specifically, the present invention relates to a device and a method for manufacturing a work which can prevent a work punched out by a main punch from being pushed back to a material to be processed side at the same time of a die opening operation, prevent the size of a die structure from increasing in the height direction, and allows an easy replacement/inspection of a biasing portion which is a driving source of an ejector.
2. Description of Related Art
Generally, a conventional pressing machine including an upper die unit and a lower die unit, one of them having a main punch and the other having an ejector that can move up and down, a biasing portion that biases the ejector in a work ejecting direction, and a position retaining portion that retains the position of the ejector which is moved against a biasing force of the biasing portion for a certain period of time is known (refer to Related Arts 1 and 2, for example). In such a known pressing machine, when the upper die unit and the lower die unit are opened from a closed state by a predetermined amount, the position retaining portion releases the ejector retained in a position and the work is punched out by the main punch and retained on the other die unit side by a frictional force is discharged by the ejector. Thus, the work punched out by the main punch is prevented from being pushed back to and interfering with a material to be processed (which is also called “push-back”) when the die units are opened.
Related Arts 1 above discloses a pressing machine, as shown in FIGS. 7 and 8, including: a lower die unit 100 having a main punch 101; an upper die unit 102 having an ejector 103 that can move up and down and an elastic member 104 connected to the ejector 103 at the top end thereof that biases the ejector 103 downward; and a position retaining portion 109 for retaining the ejector 103 in a position for a certain period of time. The position retaining portion 109 includes an ejector block 105 having one end portion engageable with the ejector 103 and being movable in a horizontal direction, a backup block 106 which is engaged with the ejector block 105 and can move up and down, and an elastic member 107 which biases the backup block 106 upward. When the upper die unit 102 and the lower die unit 100 are closed (see FIG. 7), a work W is punched out from a material to be processed M by the main punch 101. When the upper die unit and the lower die unit are opened (see FIG. 8), the ejector 103 retained by the position retaining portion 109 is released, the ejector 103 is moved down by a biasing force of the elastic member 104, and the work is discharged by the ejector 103.
Related Art 2 above discloses a pressing machine, as shown in FIGS. 9 and 10, including: an upper die unit 110 having a forming punch 111 (main punch); a lower die unit 112 having a counter punch 113 (ejector) that can move up and down and a biasing portion 114 which is communicated to the bottom side of the counter punch 113 and which biases the counter punch 113 upward; and a position retaining portion 119 for retaining the counter punch 113 in the position for a certain period of time. The position retaining portion 119 has a pusher member 115 disposed to the counter punch 113 so as to move up and down, a slider 116 which is horizontally movable, a spring member 117 which biases the slider 116 and a cam structure 118 (cam and follower) which is provided between the pusher member 115 and the slider 116 and which moves the pusher member 115 upward in an engaged state and retains it in a descended position in a non-engaged state. When the upper die unit 110 and the lower die unit 112 are closed (see FIG. 9), the main punch 111 punches a work W from a material to be processed M. When the upper die unit and the lower die unit are opened (see FIG. 10), the counter punch 113 retained by the position retaining portion 119 is released, the counter punch 113 is moved upward by a biasing force of the biasing portion 114, and the work is discharged by the counter punch 113.
[Related Art 1] Japanese Patent Laid-open Publication No. 2008-142772
[Related Art 2] Japanese Patent Laid-open Publication No. 2001-121220
However, in Related Arts 1 and 2, the biasing portion (the elastic member 104 of Related Arts 1, the biasing portion 114 of Related Arts 2) as a driving source of the ejector that discharges a work is disposed along a direction in which the ejector moves up and down, resulting in an increase of the size of a die structure in a height direction. Especially, when there is a dimensional restriction in a height direction of a die structure, a biasing portion having a smaller dimension of height (that is, a smaller biasing force) must be adopted in some cases, leading to a low flexibility in selection of a biasing portion. Further, in a case where a biasing portion is changed according to the material, shape and size of a work or a biasing portion is inspected for damage or the like, the upper die unit or the lower die unit needs to be removed from the pressing machine. This complicates replacement or inspection of a biasing portion.